The very selective and specific binding characteristics of antibodies makes these molecules extremely attractive for use in a variety of medical and basic research applications. Traditional methods for generating antibodies involve immunization and hybridoma technology for the generation of monoclonal antibodies. Recently, PCR based techniques have made it possible to engineer humanized antibodies which may serve as better therapeutic agents than their murine counterparts (Winter, and Milstein, 1991; Co, and Queen, 1991; Orlandi et al. 1989). Furthermore, this technology has progressed to the point where it is now possible to clone the immunoglobulin (antibody) repertoire of an immunized mouse from spleen cells into phage expression vectors and identify expressed antibody fragments specific to the antigen used for immunization (Winter, and Milstein, 1991; Gussow et al. 1989; Hodgson, 1991; Marks et al. 1991; Garrard et al. 1991; Duschosal et al. 1992; Kang et al. 1991b; Clackson et al. 1991; Huse et al. 1989; Persson et al. 1991; Kang et al. 1991a; Hoogenboom et al. 1991; Barbas III et al. 1991). However, this technology has had little success in identifying specific antigen binding antibody fragments from unimmunized animals suggesting that there may be a prerequisite for prior immunization to the antigen of interest.